My Panasonic Let's NOTE CF-W5KW8AXR laptop' SCREEN intermittently goes very very dark. I can just barely see the icons enough to properly shutdown or restart.

It has been doing this for a couple of days. At this very minute, the screen light has returned. It has been coming and going regularly for a couple of days. We spoke to the Panasonic service center and they said that the problem is either (1) the LCG or (2) the inverter board. The former being over $700 to repair while the latter as much as $350.

Again, it comes and goes and the screen is just barely visible with a bit of hard work / squinting.

What must it be? It is my 2nd laptop to do this. The other is a Toshiba Tecra with exactly the same symptoms.

Those can't be US dollars?
I converted Japanese yen into USD. So, yes, that is approx. in USD.Those are high prices. Here in Britain, One would expect to pay one third to one half of those prices for a typical laptop. Possibly your laptop is special in some way? It is not a model sold in Europe. HOWEVER, unless a laptop is almost new, the cost of a MAJOR repair can be GREATER than its value. Even for a cheap brand like Dell. I agree that the inverter board may be involved, or else the backlight. I am a little surprised if the LCD has to be replaced completely, unless the backlight is integral and cannot be replaced separately. Maybe a new computer would be a better investment.

How important is the portable aspect? You could buy an external LCD monitor for much less than $700.